Electrical switch contact arrangement



June 23, 1953 D, MACKEY 2,643,361

ELECTRICAL SWITCH CONTACT ARRANGEMENT INVENTOR June 23, 1953 D. MAcKl-:Y 2,643,361

ELECTRICAL SWITCH CONTACT ARRANGEMENT Filed June 29, 1949 4 sham-'sheet 2 INVENTOR laIM/d Malfa? June' 23, 1953 D, MACKEY 2,643,361

ELECTRICAL SWITCH CONTACT ARRANGEMENT Filed June 29, 1949 v ii sheets-sheet s INVENTOR Dam/d M10/key MW v ArroRNEY June 23, 1953 D; MACKEY ELECTRICAL swTTcH CONTACT ARRANGEMENT 4 endete-shut 4 Filed June 29, 1949 INVEN'r'oR azzala? Make? ATTORNEY Patented June 23, 1953 ELECTRICAL SWITCH CONTACT ARRANGEMENT Donald Mackey, Haddon Heights, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 29, 1949, Serial No. 101,966

28 Claims.

This invention relates to electrical switch contact arrangements and more particularly toy such contact arrangements for switching high frequency circuits or for simultaneously switching a plurality of circuits.

In the past considerable difficulties have been experienced with switch contacts under certain conditions. Thus where high frequency signal circuits are switched, relatively small variations in the indexing, that is, the engagement position, of the contacts give rise to inductance variation that may seriously affect the signal transfer. In standard switching type television tuners for example, the individual channels Aare selected by separate switching of high frequency circuit sections involving inductors of extremely low inductance such as are suitable for tuning to frequencies as high as 200 megacycles per second or higher. Although some degree of ne tuning or automatic frequency control is generally provided, it often happens that variations in the switch contact indexing can easily change the length of the circuit path through the contacts by .an amount suiiicient to` detune the inductance as much as one percent and make it impossible to properly receive signals in the desired cha-nnel. This is especially pronounced with respect to the sound signals which accompany the video signals and which cover a frequency range of only about 0.1 megacycle per second so that they can easily be lost.

A further objectionable feature of prior art switch contacts is characteristic of the standard knife-type or so-called self-wiping switches where a contact blade is moved between two yieldablev cooperating contact lips to engage both 4lips and spread them apart somewhat. It often happens with such switches that the blade becomes misaligned with the lips and only engages one of them giving rise toa change of inductance where high frequency signals are carried.

Other switch contact difficulties make themselves felt Where a multiplicity of switch contacts are arranged to be simultaneously engaged with selectable sets of cooperating contacts. In attempts to simplify the construction and avoid the use of carefully aligned `knife-type contacts, the use of plain dome-shaped contacts has been resorted to. However, this has the disadvantage of increasing the force required to overcome mechanical friction at the contacts and bring them into engagement. rlhis becomes so marked where a set of contacts are to be simultaneously engaged that in many cases the operato-r applies switch actuating forces violently enough to cause the switch to jump through the position at which it was intended to stop.

Among the objects of the present invention is the provision of improved switch contact ar- 2 rangements of simple construction that .avoid the above difficulties.

A specific object of the invention is improved switch contact arrangements that show reduced inductance variation in response to changes in contact engaging positions.

A further object of the invention is the provision of improved switch contact constructions for signal tuners having a multiplicity of contacts that are simultaneously engaged.

An additional object of the invention is improved turret type tuners for selecting high frequency signals and having contacts that are easily engaged and are not subject to much contact inductance variation.

The above as well as further objects of the invention will be more readily understood from the following description of exemplii'lcations thereof, reference being made to the accompanying drawings wherein:

Figure l is a side view of a television tuner embodying contact arrangement features of the present invention, with a portion broken away to show certain details of its interior;

Figure 2 is an end View of the television tuner of Figure 1, with other portions broken away to show further details of its construction;

Figure 3 is a side view of a movable selector portion of the tuner of Figures 1 and 2;

Figure 4 is an enlarged broken away detail view, partly in section, showing a pair of cooperating contacts of the tuner of Figures 1, 2 and 3, in accordance with the invention;

Figures 5 and 6 are views in elevation and plan, respectively, and partly in section, of a different form of television tuner embodying contact features of the invention, Figure 6 being taken along section line 1 1 of Figure 5;

Figure 7 is a plan view of a portion of the. tuner of Figure 5 showing certain constructional details;

Figure 8 is a View of the opposite surface of a tuner component shown in Figure 6;

Figure 9 is a schematic explanation of some of the advantages of the switch contact systems of the invention; and

Figure 10 is a fragmentary View showing a further switch oontact system embodying the invention.

According to the present invention electrical switch contacts are arranged to show reduced variations in contact inductance by having at least one of a cooperating pair of contacts in the form of a loop. The loop is connected to its associated circuit at one portion and extends at another portion along the path in which the contacts move for engagement and disengagement. The desired circuit connection is thereby established from the contact engagement point in parallel paths extending in opposite directions aeliacoi around the loop to the associated circuit. By reason of the fact that the combined length of these parallel paths is Xed, the overall inductance variation due to shifts of the contact engagernent point is greatly reduced. As the engagement point shifts lengthening one of the parallel paths, the other is shortened.

r'he present invention also includes the reduction in inductance variation at a pair of con nected contacts that are separately engageable by cooperating contacts held for simultaneous movement into engagement position. At least one oi each cooperating set of contacts is elongated along their relative path of movement and connected to its associated circuit so that a shift in engagement position increases the length of the circuit path at one cooperating set and simule taneously shortens the circuit path at the other set. By so opposing the change in circuit path lengths, inductance changes at each set also oppose each other and approximately cancel out.

A further feature oi the pesent invention is the simplied manipulation oi contacts in the form of a multiplicity ci simultaneously engaged inexpensive dome type contacts. By reducing the angle at which the cooperating contacts engage each other, the force required to bring them into engagement is also considerably reduced. This reduction is multiplied by the number of simultaneous engagements and makes a significant difference in the manipulation. Where the above type of loop contact is not used in one position of a set of switch contacts, the present invention also includes the provision or a dummy Contact to keep the loop from vibrating and thereby disturbing associated circuits.

Referring to Figures 1, 2 and 3 in which like reference characters designate like parts, a television tuner providing a television circuit switching assembly and exeniplifying one embodiment of the invention, comp-rises a box-like housing or chassis element 2li which carries on its upper or top surface 2l certain television input circuit components, including a unitary signal input matching network 25, a plurality of electrondischarge tubes 23, 29, an output inductor 3l, and a plurality or adjustable capacitors t5 and Other circuit elements such as certain inductors t5, a capacitor it and a test connection terminal element lll" are also shown as externally carried on the housing top El.

Within and partly projecting :from and below the housing 2d, a generally cylindrical selector drurn or turret Ell is rotatably held on a shaft 52 journalled in slots extending up from the lower edges of the front and rear housing walls 23. rIhe upper portion of one or these slots is shown at Eji in Figure 2. A retaining plate EEB and, retaining wire spring 5d hold and bias the shaft 52 upwardly against the top end oi the slot The plate 5t has an inwardly projecting ear anchored in a perforation lll oi wall 22, and a screw or rivet holds the plate securely against this wall. The shank of the rivet or screw Gt receives a loop @d formed on one end of spring E8, the other end of the spring being engaged in a notched flange E55 projecting outwardly from the plate r)The shalt 52 in cludes an extension having a nat for receiving an operating knob (not shown).

The drum itself is more clearly shown in Figure 3 and includes a pair oi thin, i'lat end discs till, Sit and a plurality of thin, flat intermediate discs lid, li, all being or conducting material, rigidly held on the shalt i2 in predetermined spaced relation to each other. The pe'- riphery or end disc tl' is uniformly notched (see Figure 2) to provide spaced indentations or recessed cam surfaces for engagement by a holding detent button i5 carried by a leaf spring "It suitably secured to the housing. The detent l5 may be of any suitable type such as the roundended finger or button as shown, or roller means of any well known form, for engaging the cam surfaces and intermediate notches provided on the disc Gl.

Distributed circulnerentialiy on equal radii around the discs el', 68 and adjacent their peripheries, are elongated slots or notches i8, l in aligned pairs. Each pair ci notches or slots is arranged to receive the corresponding tongued or shouldered ends 85, til or individual thin carrier strips or coil supports of insulating inaterial, five of which are shown at 39, ai, 32, 33 and 8B.

The intermediate discs lt and 'il assist in holding and locking the carrier strips securely in place. Radially projecting peripheral blades "l2 integral with discs 'iii and il are aligned in rows corresponding to the carrier strips as shown in Figures l and 3. Each oi the blades is notched in each edge as indicated at to provide an outer head or locking lug attached to the central. or body portion oi the disc, as shown more clearly in Figure 2. The body portion is connected to the blades l by a neck 'I4 at the notches E56 and around this neck the strips are held. Aligned with the disc blades or locking lugs '52, each strip has a transverse passageway or locking slot SG wide enough to receive the reduced neck portion 'ift between the notches 65 (Figure 2), but not large enough to pass the outer head or locking lug end of the blade. Each short transverse slot 3E is parallel with and opens into a longer transverse slot or passageway 8l wide enough to pass the locking lugs or heads or the blades l2. To allow longitudinal motion or" the individual strips with respect to the discs [il and t3, whereby locking to the lugs 'l2 may be eii'ected, one end oi each carrier strip is cut away, to provide shoulders Sil that fall short of spanning the distance between the end discs Eil, 553 when the other end S3 is seated in the opposite disc.

With this arrangement, the strips may readily be mounted or removed from the tuner, and rigidly held in place when mounted, as is necessary for the band change switching. Spring arms 9'! (Figure l) externally carried by the end disc E8, are provided, one for each removable unitary strip or segment, in engagement with the tongues Sil, whereby the are biased to and held in the locked position, to the left, as shown for strips 31342.52 inclusive.

rlhe separate strips each carry one or more portions of a selective signal circuit, for selecting signals in a particular frequency band or channel. The circuit portions, comprising tuning and like inductor elements, shown on strip t2 for example, are in the form of suitably shaped flat conductors provided by a conductive stratum on the non-conductive surface of the strip. Referring by way or example, to the circuit elements carried by the strip lli', these include an input tuning inductance Qi, a coupling inductance T-network including branches d2, SS and stem llt, and an oscillator tuning inductance 95. The strips also carry a set of terminal contacts |ll|- mt to which the ends of the individual inductances are connected as shown. On some of the also provide convenient means by which the strip may be grasped and moved for mounting and demounting purposes.

For some frequencies an inductor may merely be a relatively short length of straight conductor, as shown -by the oscillator inductance element or inductor 95 of strip 83, which is suitable for the standard television channel number 13. At other frequencies the inductive coating or stratum may be quite extended, as shown by the inductors of strip 84 which is highly effective with the standard television channel number 2.

For selecting signals from aV specic television channel, the drum 50 is rotated so as to bring the circuit elements of a selected one of the strips into operative connection with the remainder of the television signal-receiving system, In Figure l this connection is provided by a set of fixed contacts ||I| |8 inclusive, held on the housing 50 for cooperation with contacts of a strip at a suitable point in the rotation path of the drum. As shown, the contacts to ||8 inclusive are fixed to a non-conductive terminal board |20 held on an angularly shaped side wall plate or bracket 24 of the housing.

Referring now to Figure 4 along with the preceding gures of the drawing and particularly Figure 2, it will be seen that the movable contacts |U| to |08 are in the form of rivets which penetrate the body of the strip and have a head with a generally convex outer surface projecting out from the conductive circuit portion such as that shown at 95 in Figure 4.' A shoulder |25 on the rivet rests against the conductive stratum 95 and on the opposite face of the strip the rivet is headed over to secure the rivet or contact to the circuit element formed by the conductive stratum and to the strip. Solid or hollow rivets may be used if provided with a button head for the contact portion thereof. Y

The fixed contacts I I8 inclusive are each in the general shape of an elongated closed loop, as shown by the contact |8 in Figure 4. The loop is provided between the ends of a flat strip conductor which are joined as indicated at |22 to form a terminal whereby it is fastened to the terminal board |20 and through which it is connected to the associated circuits of the tuner. The loop is two-sided in form and presents a contact portion |24 on one side extending substantially along the travel path of a contact in each tuning section, represented by the movable contact |08, which move in either direction as shown by the arrowed lines, successively into Contact therewith. One xed contact is provided for each row of movable contacts. The xed contacts are resilient and assume the position shown by the dash lines ||9 when not in engagement with one of the movable contacts.

It will be noted that two parallel conductive paths |26, |28 extend around the two sides of the loop from the anchoring end |22 to the engaging contact |08. As a result, any displacement or improper indexing of the cooperating contacts will lengthen one path, |26 for example,

and shorten the other path |28. nasinuch as the overall loop length remains constant, the net effect is to greatly reduce thev variation in inductance otherwise caused by the change in the circuit-completing distance between the cooperating circuit sections regardless of the direction of displacement. At the high frequencies of television signals, which extend to over 200 megacycles per second, small differences in this circuit completing distance, if not counteracted, seriously change the overall inductance and may 'shift the circuit selectivity completely beyond the desired values. These small differences are of the magnitude inherent in the manufacture of the indexing mechanism including the scalloped cams 13 and the holding nose l5.

In the construction of Figure 4, a low angle of attack is provided between the movable contacts and the respective fixed contacts. As shown by the dash-line representation |09 of the head of contact |68, when the surfaces of the cooperating contacts just begin to engage, the plane of tangency is indicated by the dash-dot line |23. The angle between this line and the direction 0f motion of the movable contact represented at |24 is defined as the angle of attack. By shaping the cooperating surfaces so that the angle of attack is less than about 20 degrees, the force required to move the contacts into engagement is considerably decreased.

Because or the large number of cooperating contacts, the force required to overcome the mechanical resistance of the contacts to the rotation of the drum into any desired signal selecting step position, is a large multiple of the force required to engage an individual pair of cooperating contacts. To accurately guide and hold the drum in the selected step position, the retaining nose l5 should apply to the drum a biasing force proportional to that required to overcome the frictional resistance of the contacts, and as large as possible. In other words high contact resistance is accompanied by high bias resistance and the total force required to turn the drum then becomes considerable. As a result it often happens that the drum is actuated with such vigor that it fails to stop at the intended step, but overshoots into the next step or even into a more distant step. This makes tuning very awkward especially in view of the large number of tuning channels or steps from among which the desired one is to be chosen. With the low angle of attack the required turning force is so greatly diminished as to substantially prevent unintentional overshooting.

For delivery of the received signals selected by the tuner, a set of contact lugs |30 may be mounted to project from a wall of the housing, as shown in Figure 2. The desired circuits for further amplifying the selected signals are connected to these lugs. Some of the lugs may be used to supply operating energy to the tuner, as for example, to heat the tube cathodes and provide the energizing potentials to the tube electrodes.

Tube 28 is connected in a more-or-less conventional amplification circuit, its ampliedoutput being developed across branch 92 and stem 94 of the inductive T-network 92, 93, 94. This T-network functions to pass a selected band of frequencies to the next stage. One or more capacitors 36 may be arranged for connection in series with the coupling stem 94, and can be adjusted to series tune the coupling stem to any frequencies which it is desired not to be transferred by the T-network.

The circuit elements carried by the individual channel strips 60, 8|, 82 etc., are provided by a photo-etching process the etching portion of which may be similar to that described in U. S. Patent No. 1,582,683. The specific features of the circuit elements as Well as their preparation are not part of a present invention but are covered by the copending application of Donald Mackey, Serial No. 101,965, filed June 29, 1949.

For attaching the contacts, such as those shown at to |05 inclusive, the strips carrying the finished photo-etched circuit are punched at the desired locations and the contacts inserted and riveted in place. Before insertion, the contacts may have their circuit-engaging surfaces (|20 in Figure e) coated with a soldering composition, so that after heading over, the contacts may be heated to eiTect soldering and establishing good electrical engagement. The contact receiving sections of the circuit stratum may be enlarged to assure proper engagement regardless of some variation in the position of the contacts.

Figures to 8 inclusive show a further modiiication of a television tuner embodying the invention. Here a cast or machined generally cylindrical casing 500, open at one end and having an internal cavity 502, is pivotally mounted on a xed plate 504, as by a boss 505 in which is journalled a pin 501 secured to the plate by the threaded engagement of a reduced end 510 with a nut 5|2. The other end of the pin may have an enlarged head or cap (not shown) for retaining the casing 500 in place. The plate 554, part of which is shown broken away, overlies the open end of the casing and holds a fixed circuit board 5|4, as by spacer pins 5|5, within the cavity 502. The pins 5|6 are suitably secured at their ends, as by threaded engagement with nuts or screws or by staking them in place, that is, deforming them after insertion in a receiving aperture to provide an enlarged head. portion that prevents withdrawal.

The casing 550 houses a selector disc 520 which n is supported on one side 52| by a shoulder 530 and a ange 532 shown in Figure 5 as formed on the inner surface of the casing. Another support for surface 52| may be provided by a shoulder (not shown) on the boss 505, and if desired, A

the selector disc may be retained in place as by a spring ring (not shown) held in a groove on the boss just outside the opposite surface 522 of the disc. The selector disc itself is more completely shown in Figures 6 and 8, and is constrained to rotate with the casing by engagement of a rib 534 on the inner easing wall with a corresponding notch 536 in the disc.

According to the invention a desired signal transfer circuit having selectably interchangeable components is divided into a relatively fixed portion held on the board 5M, and a relatively movable portion carried by disc 520. The movable portion is shown in the construction of Figure 5 as including the selectable circuit elements some of which are shown in the form oi conductive stratum portions on the face 52| in Figure 6. On the opposite face 522, the disc carries additional circuit-elements as well as contacts 505 connected to the circuit elements and positioned to engage cooperating contacts SI5 held on the board 5l4, as more clearly shown in Figure 7. In this manner, by connecting contacts 5I6 through leads such as Wires 540 with the associated iixed circuit elements which may includeone or more 5 electron-discharge tubes 542 held on the board 514 or fixed plate 554, and shielded as shown, the desired circuits are completed.

Face 52| of disc 520 (Figure 6) carries a multiplicity of interchangeable sets of circuit elements each set having its own contacts 508 for eiecting the desired signal selection and transfer. It is only necessary to rotate the casing and bring the desired set of contacts 508 into engagement with the ixed contacts 5|8. The outer surface of the casing 500 in Figure 5 is in the form of a thumb wheel having ridges 544 to simplify its manual rotation. A holding device such as roller 546 resiliently carried by plate 504 holds the easing in any of the desired rotary positions by engaging a corresponding notch 548 of a set of notches cut in the edge of the casing walls. For indicating the rotatory position of the assembly, the disc may carry indicators such as slide guides 535 between which indicator cards 531, carrying suitable legends, can be slid in place and retained. The assembly can then be mounted behind a barrier 545 such as the front wall of a conventional television receiver cabinet, and the wall perforated as shown at 541 to permit penetration of the ridges and their manipulation by the iingers, and also permit observation of the proper indicator card.

According to one form of the invention, the xed contacts 5|8 on board 5|4 are ten in number as shown at 55|, 552, 553, 554,- 555, 556, 551, 556, 555 and 550 in Figure '1. These fixed contacts cooperate with the movable disc contacts 508 of an inner ring of oscillator inductanees 56|, an intermediate ring of coupling inductanees 562 and an outer ring of input inductanees 563.

The coupling inductanees 562 are connected to provide a multiplicity of T-networks one of which is identified as including a stem 565, a first branch 566 and a second branch 561. The branches of one network are spaced from each other and a branch of another network is placed between the spaced branches for the purpose of shielding the two branches of one network from each other. In Figure 6 for example, inductor 516 is interposed between branches 565 and 561, While inductor 516 forms one branch of another coupling network including stem 515 and branch 511. The remaining coupling inductors are similarly distributed in groups of four, radially around the face 52| of disc 520.

The disc contacts 565 are distributed as six concentric rings, theA inner ve rings of which contain twelve contacts, the outermost ring twenty-four. Two adjacent contacts of the innermost or iii-st ring are shown at 65|, 602 and in the second ring at 6i2, 513. Four consecutive contacts of the third ring are identified as 625, 626, 621 and Contacts 555, 561 and 648 are examples or" the fifth ring, while the sixth or outermost ring includes contacts 559, 656, 56| and 652.

Figure 5 shows the lifted contacts 55E to 565 in dash lines in the position in v-'fhich they cooperate with the disc contacts in one signal-selecting position of the disc. Fixed contacts 55| and 552 engage respectively the disc contacts 50| and 6|2 which terminate the oscillator induetor 56A. At the same time nxed contacts 553 and 554 engage the disc contacts between which the stem 565 and one branch 556 of a correspondingr coupling network are serially connected, while the free end of its other branch 561 is engaged by iiXed contact 555. For improving the shielding between the two branches 566 and 561, xed contacts 556 9, and 551 simultaneously short circuit the conductive path formed by inductors 515 and 516. The signal input circuit is completed by the engagement of fixed contacts 555 and 566 with disc contacts 569 and 666 respectively, at which the input inductor 565 terminates.

For some purposes, as when an unused inductor resonates with its self-capacitance to a frequency close to or within the frequency range of signals being received, adverse effects `are avoided by changing the connection to this unused inductor. As shown for example in Figure 6, the fixed contact 558 is positioned to ground one end of an inductor adjacent to inductor 566 but not used in the selector step illustrated. This grounding so changes' the resonance of the unused inductor as to avoid any undesired absorption of the selected signals. This expedient may be helpful on one or more of the many channels.

It will be noted that the circuit components on disc face 52| provides only six sets of signal-selecting elements. Additional sets can be applied to the opposite face 522 as shown in Figure 8. The numbered disc contacts of Figure 6 are identified in Figure 3 to show their interrelationship.

By distributing the inductors on the faces, as shown, a rotation of the disc shifts the signal selection Ato vanother set of inductors. In one step of counterclockwise rotation, as seen from Figure 6, fixed contacts 55| and 552 move respectively to disc contacts 662 and 6|3, thereby connecting to the oscillator inductor 58| on face 522. Fixed contacts 553, 555 and 555 also shift respectively to disc contacts 621, 641 and 639 to complete a connection to the coupling network including stem 515 and branches 516 and 511, all on face 526. At the same time fixed contacts 556 and 551 move to short out the disc contacts 626 and 656 to which inductor 582 (Figure 8) is connected. Even though inductor 562 is on disc face 522 opposite to the face 52| which carries coupling network branches 516 and 511, the shielding between these branches is improved by shorting it out. The shifting of the input circuit fixed contacts 559 and 560, brings them respectively to disc con- .tacts 66| and 662 which are connected to the ends of input inductor 563 on face 522.

For further improving the shielding, an `additional shorting contact may be mounted midway between fixed contacts 556 and 551, so that the inductor between and on the same face as the coupling branches being used, is always shorted. Such a combination of three closely spaced contacts may be replaced by a single wide contact if desired. Furthermore, the snorting contacts may be grounded so as to ground as well as short out the shield inductance.

Rotation of the disc 526 to the successive steps brings successively different sets of signal selecting circuit elements into the signal circuit. The sets are each arranged to impart the desired signal selectivity as by using individual inductors of the proper inductance and capacitance characteristics.

A conductive ring 585 entirely encircling the intermediate set of inductors 562 on face 52| shields them from the outer set of inductors 563. On face 522 a corresponding conductive ring 685 also eifects corresponding shielding. For further improving the shielding, the casing 566, which is itself grounded, is so shaped that flange 532 contacts ring 565 effectively also grounding this ring.

The disc 526 is itself made by a photo-etching technique as described in the above-identied copending application. The contacts may be in 10 the form of rivets staked to the disc, as described above. A fine tuning or automatic frequency control similar to that described above in connection with the construction of Figures l, 2 and 3 may also be provided.

An important feature of the invention incorporated in the construction of Figures 5 to 8 inclusive, is the improved contact arrangement. Considering the contacts for the oscillator inductors as an example, there are la pair of fixed contacts 55|, 552, and a pair of movable contacts 66| and 6 |2. The xed contacts have a loop portion 596 for engaging a cooper-ating movable contact, and a body portion 59|, .to which its associated circuit elements are connected. The contacts in each pair are held in substantially constant relative position but each pair is movable with respect to the other to simultaneously make a pair of circuit connections.

One of each of the simultaneously connected pairs, that is contacts 55| and 552, is elongated along the relative travel path of the contacts so that improper indexing or location of the contacts at the desired step position introduces substantially no inductance variations. Thus, if the disc were shifted slightly in :the counterclockwise direction, the distance from contact 66| to the body portion 59H of contact 55|, and to its iassociated circuit elements is somewhat shortened. However at the same time the path from the other` contact 6|2 to the body portion of fixed contact 552 is correspondingly lengthened, the two changes in path length substantially balance each other so that the overall eiect is negligible. Any dierences such as those due to the unequal arcs of movement of the two contacts 55| and'552 is further reduced by the loop shape of the contacting portion, as described above in connection with Figure 4.

If desired a further reduction in contact variation effects can be made, as in the outer inductances 563, by positioning the contacts along a single arc so that there is no difference in arc radius and hence equal arcuate travel by both movable contacts. The snorting contacts 556 and 551 need not incorporate any arrangement for reducing contact variation effects.

Figure 9 is a simplified diagrammatic showing that more clearly illustrates one phase of the inductance variation reducing feature of the invention. Here a support or carrier structure 25|] holds a section 252 of a high frequency circuit including contacts 254, 256. Another circuit section includes cooperating contacts 264, 256 and is held for relative movement with respect to section 252 in the direction of the arrow 266.

' Contacts 265, 266 include engagement portions 214, 216 for cooperation with the opposing contacts 255, 255 and circuit connection tabs 284, 266 by which they are connected to their circuit section. Engagement portions 214, 216 are elongated along the relative travel path of the cooperating contacts and provide a range of contact engagement positions. Connection tab 284 is spaced in the direction of arrow 260 from the engagement portion 214 and tab 286 is spaced in the opposite direction from its engagement portion 216.`

In the example of Figure 9, section 250 is shown in one circuit-completing position by the full lines. Here the circuit is completed through contact 264 by a conductive path having a length indicated at A. A corresponding circuit-completing path along contact 266 is indicated at B.

With variations in the indexing of the conlli tacts these paths change in length and for high frequency signals contribute changes in inductance. The remaining portions oi" the circuit need not be considered inasmuch as they are not varied by the switching action. The dash line showing of section Z shows anothel1 engagement position in which the paths along the elongated contacts have been changed in length. These changes may be inherent in the mechanical switching position tolerance of the apparatus upon which the sections are carried.

The orientation of the elongated contacts, in accordance with the invention, causes any change in length at contact 26d, as for example from A. to C, to be opposed by the corresponding change simultaneously effected at contact 216 from B to D. As one contact path becomes longer, the other becomes correspondingly shorter. Stated diierently, the geometric relationship assures the minimizing of overall contact inductance variations caused by shifts in contact engagement.

Figure l shows another switch contact arrangement embodying the invention. Here an inductance-holding carrier sheet 390 is mounted on a slidable support 3M; for simple translational movement as indicated by the doubleheaded arrow 330. The support 340 is in the general shape of a channel having inwardly directed side flanges 352 on which the carrier is held as by rivets or screws 344. The carrier 309 has a plurality o1 sets of inductors 35H distributed in transverse rows and connected to contacts 303 in a manner similar to those on the individual strips 80, 3i etc. of the construction of Figures 1, 2 and 3, but here carried by an integral carrier sheet. Slots 350 are provided between some of the individual inductors in the same set. Struck up from the web of channel 390, are electrically conductive shielding `tabs 345 which pass through the slots 350 and provide shielding` where desired. The entire channel 340 may be made from a strip of metal suitably bent into shape.

A terminal board 32e is held on nxed side supports 324 and carries a transverse set of stationary contacts 3H to inclusive for engagement by the individual transverse rows of inductor contacts 308 on the sheet 390. Suitable guide structure which includes the side supports 324 engages the channel and assures the alignment of the cooperating contacts. The terminal board 32D may also carry some or all of the additional tuner circuit components including electron-discharge tubes.

The contacts Sil-3HE include elongated engagement portions 360 and connection portions 362, and are oriented in the direction 330 so that indexing changes in the circuit of any inductor occur in pairs and oppose each other to minimize overall inductance variations. In the construction of Figure 10, any indexing change is the same at all the elongated contacts 3Il3|8 so that overall changes in length are substantially exactly balanced out.

Although the present invention has been described above in connection with television tuners, the inductance variation reducing feature can also be embodied in apparatus for transferring any high frequency signals, such as those as low as 2 megacycles per second or as high as 1000 megacycles per second.

The various features of the invention need not all be combined in the same construction. Thus the improved low angle of attack switch Contact feature contributes its important advantages to low or high frequency circuits where a decrease in mechanical switching forces is desirable. Similarly the dummy contact arrangement is highly effective for suppressing undesired microphonic or vibratory effects in al1 types of circuits, particularly where there are resilient contacts that have relatively easily vibratable portions such as the inductance-reducing loops of the invention.

As a further exemplication of the invention the turret construction of Figures l, 2 and 3 can be combined with the oriented contact feature of the construction of Figure 10. This is effected by either reorienting the stationary contacts lII-I I8 cooperating with the drum type turret 50, or by bending the carrier sheet 390 into the form of a cylinder and mounting it for rotation around the longitudinal axis of the cylinder.

The present invention is not restricted to any specic forms of circuit components. Thus for example the switched circuit sections may have one or more inductors in the form of standard windings or coils of wire, or these sections may be devoid of inductors and only include capacitors or other circuit elements. Combinations of all types of circuit elements can also be used.

The dielectric or substantially non-conductive material forming the circuit-carrying structure of the invention may be of any convenient composition. When the circuit elements are carried as conductive coating `portions the carrier or support sheet should not contribute any appreciable losses to the circuit. Phenol-formaldehyde resins are highly effective, and may include powdered mica ller if desired. Where the carrier is to be bent to any signicant degree, as for the integral drum construction prepared from the carrier of Figure l0, less brittle compositions such as polyethylene. (highly polymerized ethylene) or polystyrene (highly polymerized styrene) are more suitable. These more flexible materials can also be further flexibilized by the incorporation of standard plasticizers.

Substantially any metal can be used to form the circuit elements such as the conductive strata of the invention. Copper and silver are preferred inasmuch as they combine high electrical conductivity with low corrosion and relatively low cost. .Aluminum can also be used. Zinc is satisfactory but is improved by a protecting layer such as varnish, to reduce its corrosion under atmospheric influences.

While several exemplifcations of the invention have been indicated and described above, it will be apparent to those skilled in the art that other modifications may be made without departing from` the scope of the invention as set forth in the appended claims.

What is claimed is:

l. In a high frequency electric signal selecting system for selectably transferring signals in any of a. multiplicity of high frequency signal channels in the 2 to 1000 megacycle per second irequency range: signal transfer apparatus having a relatively stationary section and a relatively movable section; channel-selecting inductor elements and a set of electrical contacts on one of said sections; a set of electrical contacts on the other section each contact being positioned to engage a different one of tlhe inst-mentioned contacts; means for moving `the contacts into engagement; at least one of the engaging contacts comprising a conductive loop connected with its associated network section at one portion and having another portion extending substantially along the travel path of the engaging contact for establishing electrical engagement through a pair of inductive paths oppositely dinected along the loop and electrically in parallel, the combined length of said paths being constant and the overall inductance being accordingly subject to reduced variation resulting from shifts of the contact-engagement posi-tion along the loop.

2. In a high frequency electric signal selecting system for selectably transferring signals in any of a multiplicity of high frequency signal channels in the 2 to 1000 megacycle per second frequency range: signal transfer apparatus having a relatively stationary section and a relatively movable section; interchangeable channel-selecting inductor elements and a set of electrical contacts on one of said sections; a set of electrical contacts included in the other section and positioned to engage the first-mentioned contacts and establish the desired signal selection when moved into the corresponding cooperative relation; means for moving the contacts into corresponding cooperative relation at least one of the engaging contacts for each inductor element being in the form of a conductive loop connected with its associated section at one portion and having another portion extending substantially along the travel `path of the cooperating contact for establishing electrical engagement through a pair of inductive paths oppositely directed along the loop and electrically in parallel, the combined length of said paths being constant and the overall inductance being accordingly subject to reduced variation resulting from shifts of the contact-engagement position along the loop.

3. In a turret type television tuner: signal transfer apparatus having a relatively stationary circuit section including stationary contacts, and a relatively movable circuit section; means holding the relatively movable section on the turret; a plurality of separate interchangeable sets of signal-selecting inductors included in said movable section, each inductor having contacts for interchangeably connecting the sets with the fixed circuit section to provide selectable transfer of the desired signals; means for moving said movable section along a travel path providing engagement between the said contacts; at least one of the connecting contacts for each inductor element comprising a conductive loop connected with its associated circuit section at one portion and having another portion extending substantially along the travel path of the cooperating contact for establishing electrical engagement and conduction from the point of engagement through a pair of inductive paths oppositely directed along the loop and electrically in parallel, the combined length of said paths being constant and the overall inductance of each inductor being accordingly subject to reduced variation resulting from shifts of the contact-engagement position along the loop. Y

4. 'Ithe combination as defined by claim` 3 in which there is further included holding structure connected for yieldably holding the turret in an individual channel-selecting position, and the contacts of at least one section having generally dome-shaped engagement surfaces with angles of attack of not more than about 20 degrees for (illv 6. Tlhe combination as defined by claim 17 in which the relative travel path of the first contacts corresponds substantially exactly to the relative travel path of the second contacts thereby substantially balancing out contact inductance variations.

7. In a television tuner: a signal transfer network having a relatively fixed circuit section including rst and second contacts, and a relatively movable circuit section having rst and second contacts; means providing engagement of the movable circuit contacts with the corresponding iixed section contacts along a relative travel path between said circuit sections an elongated conductive surface on one of said first contacts along the relative travel path to bring this contact into engagement with its corresponding contact along a range of engagement positions; an elongated conductive surface on one of said second contacts along the relative travel path to also bring this contact into engagement with its corresponding contact along a range of engagement positions; connections from said elongated surfaces to their circuit sections at those portions of their elongated surfaces which cause variations in the engagement positions of the sections to introduce variations in circuit length at the first contacts that oppose variations in circuit length at the second contacts thereby reducing the overall variation in contact inductance.

`8. The combination as defined by claim 7 in which the elongated contacts each comprise a conductive loop extending substantially along the relative travel path of engagement thereby providing conductive paths electrically in parallel and oppositely directed along each loop, the parallel paths further having a fixed combined length whereby the overall inductance between the circuit sections is subject to reduced variation from shifting contact engagement positions along said loop.

9. In a circuit switching system for selectably establishing any of a plurality of electric circuits: a pair of relatively movable and connectible circuit sections; contacts on each section positioned to engage each other for establishing the individual circuits; individual sets of contacts lon one of said sections, each set being connected for establishing a different one of the circuits at different relative positions of the circuit sections; a pair of conductive paths from the engagement position to the circuit sections of a portion of the contacts; holding structure connected for yieldably holding the movable circuit section in the individual circuit-selecting position; and contact mounting structure providing engagement of said contacts with angles of attack of not more than about 20 degrees thereby reducing the holding and moving forces required to shift the circuit selection.

10. The combination as defined by claim 9 in which at least one of the contacts comprises a loop conductor connected at one portion to its associated circuit section and extending at another portion substantially along the travel path of the engaging contact thereby establishing a iii circuit connection through the conductive paths oppositely directed along the loop and electrically in parallel, the combined length of said paths being constant and the overall inductance of said paths being accordingly subject to reduced variation resulting from shifts of contact-engagement position along the loop.

l1. In a turret type television tuner: a signal transfer network having a relatively fixed circuit section including fixed contacts. and a relatively movable circuit section; means holding the relatively movable section on the turret; a plurality of separate sets of signal-selecting inductors in said movable circuit section; contacts on each inductor having parallel conductive paths from the point of engagement to the inductor, said contacts for interchangeably connecting the sets with the iixed circuit section to provide select able transfer oi the desired signals; and holding structure connected for yieldably holding the movable circuit section in the individual circuit- .selecting position.

12. The combination as defined by claim ll in which first and second inductor contacts are connected for engaging lirst and second contacts of the relatively xed circuit section; one of said first contacts being elongated along its relative travel path to bring it into engagement with the corresponding contact along a range of relative positions, and one of said second contacts being elongated along its relative travel path to also bring it into engagement with the corresponding Contact along a, range of relative positions; connections between said elongated contacts and their circuit sections at those portions of their elongated lengths which cause variations in circuit length at the rst contacts that oppose variations in circuit length at the second contacts thereby reducing the overall variation in contact inductance; and said elongated contacts comprise i a conductive loop said loop extending substantially along the relative travel path of the engaging contact for providing circuit connections through paths electrically in parallel and oppositely directed along each loop, the combined length of the parallel paths being fixed and the overall inductance Variation of the loop engagement being accordingly further reduced.

13. In a circuit switching system for selectably establishing any of a plurality of electric circuits: a pair of relatively movable and connectible circuit sections contacts on each section positioned to engage each other for establishing the individual circuits; individual sets of contacts on one of said sections, each set being connected for establishing a different one of the circuits at different relative positions of the circuit sections; a set of loop-shaped contacts on the other of said sections each with resilient loop portions extending along the relative path of travel of the engaging contacts of the individual sets for yieldable engagement of some of the loops with the contacts of the individual sets to complete the individual electric circuit; dummy contacts on the individual sets for engaging the balance of the loops and reducing microphonic tendencies due to vibration of the yieldable loop structure of the 1oopshaped contacts; and means for relatively moving the sections and thereby moving the resilient loop portions into engagement with the individual sets of contacts to establish a different one of the circuits at different relative positions of the circuit sections.

14. In a circuit switching system of a signalreceiving circuit for establishing high frequency 16 signal connections between a portion of a signal circuit and the remainder of said signal-receiving circuit, the combination comprising rst contact means connected to the portion of said signal circuit, second ycooperating contact means connected to the remainder of said signal-receiving circuit, means for providing relative movement between the different contact means and providing a range of contact engagement positions, thereby establishing said high frequency signal connections, one of said contact means having contacts with an elongated contact portion extending substantially along the travel path of said relative movement, connection tabs for said last mentioned contacts, two parallel conductive paths of iixed length extending from the end of the elongated contact portions to said connection tabs and oriented to cause any changes in path length to substantially balance each other thus greatly reducing variations in contact inductance due to shifts of the Contact engagementl points by thereupon causing one conductive path to become longer as the other becomes correspondingly shorter.

l5. The combination as dened by claim 14 in which each contact means includes a pair of contacts, one pair of contacts has the elongated contact portion, and each one of said last mentioned contacts is connected to the corresponding connection tab by one of the paths, said paths extending in opposite directions from the engagement portions.

16. In a circuit switching system for establishing an electric circuit for high frequency signals: a pair of connectible circuit portions, each having an electric contact; means for moving one circuit portion with respect to the other thereby to engage said contacts and provide an electrical connection between said circuit portions; means providing in combination with one of the contacts a conductive loop connected to its associated circuit portion at one position, a portion of said means extending substantially along the relative path of movement of the other contact, the conductive loop thereby comprising a circuit connection through a pair of inductive paths along the loop extending from the point of engagement of the contacts and electrically in parallel, said paths having a combined length that is constant whereby the overall inductance between said circuit sections is accordingly subject to reduced variation resulting from shifts of the contact engagement position.

17. In a circuit switching system for establishing an electric circuit for high frequency signals: a first tuned circuit portion including rst and second electrical contacts; a second circuit portion adapted for tuning by said rst circuit portion including first and second electrical contacts; means for moving the sections with respect to each other along relative parallel travel paths adapted to bring their respective contacts into engagement along a range of positions; an elongated contact portion provided for one of said nrst contacts along the relative travel path to bring the corresponding contact into engagement therewith along said range of engagement positions, and a further elongated contact portion provided for one of said second contacts along the relative travel path to also bring the corresponding contact into engagement therewith along a like range of engagement positions; and means providing a pair of conductive paths for said elongated contact portions extending rcspectively from the engagement position to the 17 corresponding circuit portions to thereby reduce variations resulting from shifts of the contact engagement position.

18. In a switching system having switch contacts movable over a relative travel path, a high frequency switch comprising a contact elongated caused by shifts of the contact engagement position, a xed contact, a movable contact, indexing means for moving said movable contact into engagement with said fixed contact along a relative travel path between the contacts, an engagement portion on one of said contacts elongated along the relative travel path and providing a range of contact engagement positions, and means minimizing inductance variations of the contacts caused with variations of the indexing comprising a pair of contact paths so oriented that one contact path becomes longer as the other becomes correspondingly shorter.

20. In a high frequency signal-receiving system the combination comprising, an inductance comprising a conductive stratum on a non-conductive strip, a pair of electrical contacts connected to said inductance, means including a pair of cooperating contacts for selectively bringing the inductance into operative connection with the remainder of the high frequency signal-receiving system, said means providing engagement between said contacts, and means for minimizing inductance variations caused by engagement of the contacts at different positions comprising a pair of parallel electrical paths on each contact of one pair and extending from the normal engagement position of the contacts in opposite directions thereby comprising an elongated engagement portion.

21. A system as dened in claim 20 wherein a plurality of the non-conductive strips are distributed circumferentially on equal radii around a rotational axis, and the pair of electrical contacts project radially outwardly a substantial distance from the outer surface of the strip thereby providing a positive switching connection and preventing any engagement of the stratum with the cooperating contacts.

22. A system as dened in claim 20 wherein a shoulder is provided between said electrical contacts and the conductive stratum thereby providing an enlarged conductive surface which rests against the stratum.

23. In a high frequency circuit switching system the combination comprising, a rotatable turret, a plurality of portions of a selective signal circuit mounted on said turret -for rotation therewith, a plurality of sets of movable switch contacts each set being connected to one of said circuit elements, a set of xed switch contacts adapted for connection in an electronic circuit at an anchoring end and held for cooperation with the movable switch contacts at a suitable point in the rotation path of the turret, some xed contacts in said set comprising an elongated closed loop providing two parallel electrically conductive paths from the anchoring end to the engaging contact position, a carrier strip for each set of said movable contacts, indexing means providing selective engagement of said xed and movable contacts upon rotation of said turret, and intermediate discs on said turret holding and locking the strips securely in place whereby constant engagement pressure is maintained for the contacts upon the set.

24. A switching device for high frequency circuits comprising in combination a rst contact, a second contact, indexing means providing engagement of said contacts along an extended range of Contact engagement positions, terminal connections at an anchoring end of said contacts, a conductive path from the anchoring end to each of said contacts, and means providing a second parallel conductive path from the engagement surface of one of said contacts to the corresponding terminal connection, whereby inductance variations of said device caused by variations of indexing are minimized.

25. A high frequency switch contact comprising in combination, an elongated electrical con- Ytact adapted for electrical engagement with a mating contact along a range of contact engagement positions along a travel path of a cooperating contact, a terminal connection point at an anchoring end of said elongated contact, and means providing parallel conductive paths from opposite ends of the travel path to the terminal connection point, thus minimizing inductance variations oi the contact caused by variations in engagement position.

26. In a high frequency signal-selection system, a switch comprising, a carrier structure holding a section of a high frequency circuit including a pair of contacts, another circuit section including a pair of cooperating contacts held for relative movement with respect to the rst mentioned section, engagement portions on the cooperating contacts elongated along the relative travel path and providing a range of contact engagement positions, conductive contact paths completing the circuit from each elongated portion, and orientation of the elongated portions to cause any change in length of the contact path of one of the contacts to be opposed by the corresponding change of contact path simultaneously effected at the other contact.

27. A switch as dened in claim 26 wherein the conductive paths from the elongated portions are oppositely extended from the contact engagement position along the direction of relative movement.

28. A switch as dened in claim 27 wherein each of the elongated portions is part of a loop shaped contacting portion, thereby further reducing any differences in path length due to unequal arcs of movement of the contacts.

DONALD MACKEY.

References Cited in the flle of this patent UNITED STATES PATENTS Number Name Date 2,067,395 Hand Jan. 12, 1937 2,188,829 Clark Jan. 30, 1940 2,409,617 Elliott et al Oct. 27, 1946 2,413,148 Martin Dec. 24, 1946 2,417,967 Booe Mar. 25, 1947 2,496,183 Thias et al Jan. 31, 1950 2,501,456 Thias et al Mar. 2l, 1950 2,506,727 Mas May 9, 1950 2,545,681 Zepp et al. Mar. 20, 1951 

